1. Field of the Invention
The present invention relates to a level shift circuit used for a semiconductor integrated circuit for example, and more particularly to a technology to increase the speed of operation of the level shift circuit.
2. Description of Related Art
In some cases a plurality of types of circuits are installed on one electronic equipment or on one circuit board. In such a case, signals are transmitted/received between each circuit. In the case of digital signals, two types of values, that is, low level or high level, are transmitted/received. The value of low level is often zero volts. And the value of high level is for example 1.5 volts, 3 volts and 5 volts. In some cases circuits with different high level values coexist on one electronic equipment or on one circuit board. Given such cases, a circuit at the transmission side or a circuit at the reception side must convert the high level values. If the high levels are not converted, the circuit at the reception side may recognize a high level as a low level in error.
A level shift circuit is a circuit for converting the high level voltage of digital signals. For example, signals where the high level is 1.5 volts and the low level is zero volts can be converted into signals where the high level is 3 volts and the low level is zero volts by the level shift circuit.
The level shift circuit is required to have a sufficient voltage shift amount. For example, 1.5 volt input signals must be converted to 3 volts, 5 volts or a higher voltage.
Recently the demand for high-speed operation of a circuit is strong. Therefore it is also demanded that the level shift circuit be designed so as to operate at high-speed.
Also recently the demand for the low power consumption of circuits is strong. Therefore it is also demanded that the level shift circuit be configured so as to decrease power consumption.